1. Field of the Invention
The present invention relates to a magnetic head.
With the increase of the recording density in a magnetic recording medium, the coercive force of the recording medium is increased. As magnetic heads for recording on the recording medium of the above kind, there have been proposed magnetic heads having core portions opposing the magnetic gap formed with high magnetic flux density materials.
In accordance with the present invention there is proposed a magnetic head half comprising a core base unit having a side face opposing the magnetic gap, the side face being slanted relative to the gap and a magnetic thin film made of magnetic materials of a high magnetic flux density, fitted on the side face of the core base unit opposing to the magnetic gap.
2. State of the Art
As shown in FIGS. 1, and 2 a proposed magnetic head comprises a first core half 1 and a second core half 2 and a coil 3 wound around the first core half 1. The first core half 1 and second core half 2 are made of ferrite and each of them is provided with a core base unit 5 with a projected portion 4 formed in the central part of the side surface opposing to the magnetic gap and a thin magnetic layer 6 made of high magnetic flux density material fitted on the respective side surface. As shown in FIG. 1, the projected part 4 of the first core half 1, the magnetic thin layer 6 and the projected part 4 of the second core half 2 are generally symmetrically disposed relative to the magnetic gap.
The magnetic head mentioned above is manufactured in such a manner as described below. As shown in FIG. 3, pairs of parallel groove 8 are formed on one face of a ferrite block 7 forming the core base 5 and tapered ribs 9 are formed between the grooves 8. The magnetic thin layer 6 is formed on the surface of the ferrite block 7 on which the grooves 8 and ribs 9 are formed in an uniform thickness by means of vaporizing or spattering with a high saturation magnetic flux density material. Subsequently, as shown in FIG. 5, a reinforcing layer 10 of a non-magnetic material is thickly made on the magnetic layer 6. The reinforcing layer is ground to the level shown by the dotted line. The sharp top part of the ribs 9 are ground so as to form the flat face 11. A coil slot 12 (FIGS. 2 and 8) is defined to a predetermined depth in a direction perpendicular to the rib 9. One block having the coil slot 12 and another block without a coil slot are assembled together by glass bonding so that the reinforcing layers 10 oppose each other as shown in FIG. 9. The block 7 is sliced along the dotted lines to provide magnetic heads. The magnetic heads, as mentioned above, are usually directed to the recording heads for a relatively narrow recording track of 10 .mu.m width, such as VTR. In order to provide the magnetic heads for the narrow track, the top angle .theta.1 of the projected part 4 of the base 5 is defined by a small angle between 45.degree. to 90.degree.. With the small angle .theta.1, the error of the width of the flat portion 11 can be decreased even if the amount of the grinding of the tapered part of the magnetic layer 6 is changed during grinding of the magnetic layer 6 so that magnetic heads for forming the narrow recording track can be manufactured.
However, when the magnetic head mentioned above is used in a magnetic recording device for a magnetic disc with a relatively wide track width of 40 to 200 .mu.m, the following problems occur.
In order to make the track width wide, it is necessary to increase the width of the flat portion 11 of the magnetic thin layer 6, therefore, the magnetic layer must be thick so long as the flat portion 11 is formed by grinding the tapered edge portion. When the angle .theta.1 of the projection 4 of the core base 5 is an acute angle, it takes a long time to form the magnetic layer 6, thereby decreasing the productivity of the magnetic heads and increasing the production cost. With the thin magnetic layer, the desired track width can not be obtained.
In addition in the prior art magnetic heads, since the coil slot 12 is defined after the magnetic layer 6 is formed on the ferrite block 7, the magnetic layer is eliminated at that part where the coil slot 12 is defined. Accordingly, the exciting magnetic flux developed by the current of the excitation coil 3 is introduced into the magnetic layer 5 through the core base 5 made of ferrite, thus the magnetic efficiency is reduced. Furthermore, in defining the coil slot 12 by machine cutting, the magnetic layer 6 is apt to be peeled from the core base 5 by the external force caused by the machine cutting thereby decreasing the yield of the magnetic heads.
Furthermore, it is proposed to define the thickness T of the magnetic layer 6 to be less than one half of the width of the flat part 11 which corresponds to the track width. This proposed arrangement decreases the thickness T of the magnetic layer 6, thereby causing the portion apart from the magnetic gap to be magnetically saturated prior to the magnetic saturation of the magnetic gap near the flat part 11. Accordingly, the advantage of employing a magnetic material of high magnetic flux saturation density is decreased.
Furthermore, in case the magnetic head is made for the VTR with the track width less than 10 .mu.m, the thickness of the magnetic layer 6 must be less than 5 .mu.m, which is difficult to form at a uniform thickness. If the magnetic layer has a fault, it causes magnetic saturation.
Also with the acute angle of the rib 9, crack or fault tend to occur in the tapered part of the rib when the first core half 1 and second core half 2 are manufactured. In order to avoid the crack as mentioned above, a magnetic core as shown in FIGS. 10 and 11 has been proposed.
The magnetic core shown in FIG. 10 is provided with a rib 53 having a rectangular shape in cross section at the end portion of the projection 52 of a core base 51 of a core half 50. A magnetic layer 54, similar to the magnetic layer 6, is formed in the side face of the projection 52 including the rib 53. In the magnetic head shown in FIG. 10, the mechanical strength of the rib 53 is weak and the rib 53 tends to be broken, therefore the yield of the magnetic head shown in FIG. 10 is low.
The magnetic core shown in FIG. 11 is provided with relatively wide flat parts 61 and 62 having a width t at the end of projected parts 59 and 60 of the core bases 57 and 58 of the core halves 55 and 56. The thickness of magnetic layers formed on the flat parts 61 and 62 is thinner than the magnetic layers 63 and 64 formed on the other parts while 65 denotes a magnetic gap. In the magnetic head shown in FIG. 11, the end portions of the projections 50 and 60 near the magnetic gap 65 are easily saturated and the magnetic head shown in FIG. 11 can not be used.